1. Technical Field of the Invention
The present invention relates generally to a solenoid valve and a fuel injector which may be used to inject fuel into an internal combustion engine for automotive vehicles, and more particularly to a simple and compact structure of a solenoid valve designed to keep an air gap between a stator and an armature at a constant interval required to ensure a normal operation of the solenoid valve and a fuel injector using the same.
2. Background Art
In general, a solenoid valve is used in fuel injectors for internal combustion engines. In order to avoid a failure in operation of the solenoid valve caused by residual magnetism or remanence after the supply of current to a coil is cut off, an air gap is provided between a stator and an armature. In the following discussion, a clearance remaining between a stator and an armature after a valve member is lifted up fully will be referred to as an air gap.
U.S. Pat. No. 6,027,037, issued on Feb. 22, 2000, assigned to the same assignee as that of this application discloses a solenoid valve used in an accumulator fuel injection apparatus for diesel engines which is schematically illustrated in FIG. 7.
An armature disk 104 has a protrusion 103 projecting from the center thereof to a stator 101 to form an air gap H between the armature disk 104 and the stator 101. A needle valve 107 which is lifted up and down along with the armature disk 104 is supported by a radial bearing 105 installed in a housing 106.
The above structure, however, needs to minimize the play of the needle valve 107 in order to ensure the air gap H required to avoid the failure in operation of the solenoid valve due to the remanence by designing the bearing 105 to be long and machining the bearing 105 and the needle valve 107 accurately so that the clearance therebetween will fall within a range of 5 to 10 xcexcm. The increase in length of the bearing 105 will result in an increase in overall size of the solenoid valve. The accurate machining of the bearing 105 and the needle valve 107 will increase manufacturing costs of the solenoid valve.
Moreover, because of a small height of the protrusion 103, a shift in reciprocating path of the needle valve 107 and the armature 104 may cause an outer edge of the armature 104 to hit on the bottom of the stator 101 when the armature 104 is attracted by the stator 101, thereby resulting in a variation in air gap H in the circumferential direction of the armature 104, which will contribute to a failure in operation of the solenoid 102.
It is therefore a principal object of the invention to avoid the disadvantages of the prior art.
It is another object of the invention to provide a small-sized solenoid valve designed to ensure the air gap between an armature and a stator with simple arrangements and a fuel injecting apparatus using the same.
According to one aspect of the invention, there is provided a solenoid valve which may be used in a fuel injector for automotive vehicles. The solenoid valve comprises: (a) a housing in which a valve hole is formed for blocking and establishing fluid communication between an upstream and a downstream portion of a fluid passage; (b) a valve member disposed in the housing slidably to close and open the valve hole selectively; (c) an armature connected to the valve member to be movable along with the valve member; (d) a stator disposed within the housing, the stator working to attract the armature in a direction to open the valve hole; (e) a coil producing a magnetic attractive force through the stator when energized; and (f) a spacer provided between the stator and the armature to keep a given air gap therebetween without any hit of the armature on the stator, the spacer being provided on a peripheral portion of one of the stator and the armature.
In the preferred mode of the invention, the spacer is made of the same material as that of at least a portion of the armature and formed integrally with the armature in an annular form.
The spacer may also be made of a solid film harder than the armature and fixed on the peripheral portion of the armature.
The spacer may alternatively be made up of a plurality of discrete members disposed on the peripheral portion of the armature.
The spacer may alternatively be made of the same material as that of at least a portion of the stator and formed integrally with the stator in an annular form.
The spacer may alternatively be made of a solid film harder than the stator and fixed on the peripheral portion of the stator.
The spacer may alternatively be made up of a plurality of discrete members disposed on the peripheral portion of the stator.
A bearing member may further be provided which supports the valve member slidably.
According to another aspect of the invention, there is provided a fuel injector which may be used to inject fuel into an internal combustion engine for automotive vehicles. The fuel injector comprises: (a) a nozzle valve working to open and close a spray hole selectively; (b) a nozzle body supporting the nozzle valve slidably; (c) a pressure chamber producing therein a fuel pressure working to urge the nozzle valve in a spray hole-closing direction; and (d) a solenoid valve working to control the fuel pressure in the pressure chamber. The solenoid valve comprises a housing in which a valve hole is formed for blocking and establishing fluid communication between an upstream and a downstream portion of a fluid passage, a valve member disposed in the housing slidably to close and open the valve hole selectively, an armature connected to the valve member to be movable along with the valve member, a stator disposed within the housing, working to attract the armature in a direction to open the valve hole, a coil producing a magnetic attractive force through the stator when energized, and a spacer provided between the stator and the armature to keep a given air gap therebetween without any hit of the armature on the stator. The spacer is provided on a peripheral portion of one of the stator and the armature.